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AMD’s QuadFX (a.k.a. 4×4) disappoints

The reviews are in, and 4x4 doesn't look so hot. I take a close look at the …

Today, AMD officially launched their much-anticipated 4x4 enthusiast platform under the name QuadFX. The results of the rash of QuadFX reviews that just came out are uniformly disappointing; Intel's quad-core offering, the QX6800, outperforms AMD's much hotter, more power-hungry offering in almost every benchmark. Right now, QuadFX is a loser from a performance, power consumption, and bang/buck perspective, and there's pretty much no reason to even consider spending money on this boutique architecture right now.

As grim as the picture is for QuadFX, there are a few small bright spots. But before I talk about those, I want to take a moment to recap the specifics of what has been announced today.

The QuadFX motherboard

The foundation of today's announcement is a new motherboard from Asus, the dual-socket L1N64-SLI WS, which is based on the 680a SLI chipset from NVIDIA. The 680a SLI supports AMD's Socket F, a socket format normally reserved for Opteron processors but which AMD will use in the QuadFX platform. The motherboard should run about $300, and it remains to be seen if other motherboard manufacturers will give the new platform a shot.

The NVIDIA's 680a SLI chipset actually consists of two identical 570 chipsets ganged together to offer the system a total of two x16 PCIe lanes, two x8 PCIe lanes, eight x1 PCIe lanes, four GigE ports, and a ton of other I/O options. In the interest of keeping the price down and sticking to the ATX form factor, Asus implemented only a subset of the available I/O options.

The 680a SLI is connected to one of the processor sockets via a pair of x16 cHT links, and the second processor socket is connected to the first processor socket.

The choice of an NVIDIA product for the chipset at the heart of the QuadFX launch was surprising for some, but AMD was working on "Quadfather" well before the ATI merger. There can be no doubt that there's an ATI-based QuadFX chipset product now in the works at the newly merged company, but 4x4 may well flop before that product comes to market. I hope not, though.

Whatever it is that AMD/ATI are working on, it should be much simpler and cheaper to implement than the feature-bloated 680a. The combination of two 570's yields way too much chipset hardware on the 680a. This bloat is especially tragic in light of the potential for a "lean and mean" chipset design given by the Athlon's on-die memory controllers and coherent HyperTransport bus protocol. All that QuadFX really needs in the way of a chipset is a basic southbridge.

The chips

AMD has released the following processors, sold as pairs, for use in QuadFX systems:

Model Number

Clockspeed

L2 Cache

Price (per pair)

FX-74

3GHz

2x1MB

$999

FX-72

2.8GHz

2x1MB

$799

FX-70

2.6GHz

2x1MB

$599

At these prices, it's now significantly cheaper to get these processors in Socket F format than it is to get their Socket AM2 counterparts.

Given AMD's history of supply problems, you might wonder if they'll be able to keep enough of these in the channel to meet the QuadFX demand. Unfortunately, given QuadFX's poor showing at today's debut, I don't think that excessive demand for QuadFX systems will be a problem in the near-term.

The results

If you read the reviews linked below in our "Further reading" section, you'll see that Intel's quad-core QX6700 (a.k.a. Kentsfield) pretty handily beat the top-end QuadFX system on every test but one or two meaningless synthetic benchmarks.

It's also the case that Intel's as-yet unannounced Core 2 Quad Q6600, a non-"Extreme" version of the QX6700 with a lower clockspeed and lower price, beat the top-end QuadFX system in most of the benchmarks.

So right now, if you want four cores in your system, the QX6700 (or a two-socket Woodcrest box) is still the way to go.

In many benchmark runs, the QuadFX systems couldn't even compete with dual-core offerings from both Intel and AMD. Dual-core Intel products like the E6700 beat the QuadFX platform on a number of occasions, as did dual-core Socket-AM2 products from AMD. Indeed, the new QuadFX platform came out at the very bottom of the benchmark pack too many times to make it a real contender for anyone's dollars right now.

A closer look at the results

If you've been following my 4x4 coverage, you know that I was excited about 4x4 and I consistently entertained the possibility that a 4x4 system might outperform a Kentsfield quad-core system on some types of highly multithreaded, bandwidth-intensive benchmarks, like 3D rendering and video editing. My basic line of reasoning, which I've repeated in a number of posts, is pretty well summed up in the following paragraphs from this post:

These four-core Kentsfield parts will go head-to-head with AMD's 4x4 systems. I think these two very different system architectures are going to offer a very interesting and stark choice for system builders. With four cores sitting on a single 1066MHz FSB, Kentsfield is going to have much lower per-core memory and FSB bandwidth than the comparable 4x4 system. For its part, the 4x4's two-socket design offers much higher per-core bandwidth that should give it a significant edge in bandwidth-intensive applications.

Complicating this picture is the fact that Kentsfield's individual cores will outperform the individual Athlon 64 FX cores by a significant margin. So the Kentsfield systems will have more total CPU horsepower than the 4x4 competition, but the CPU will be sipping code and data through a relatively thin straw. (See this post for more on these kinds of bandwidth issues in quad-core systems.)

My prediction is that when these two types of four-core systems are benchmarked against each other, the results are going to vary with application type to a much higher degree than reviewers have so far been accustomed to.

So did the results vary by application type, as I predicted? Well, they did indeed, but the bad news is that these variations never included a QuadFX system actually beating a top-end Kentsfield system. Still, the variability in the benchmark results matters, and it's worth looking into further.

Games, and other apps with low levels of multithreading

For gaming, the outlook for 4x4 has always been quite clear. In a post this past August, I gave the following prediction that turned out to be right on the money:

So is the gaming world ready for quad-core? In a word, no. My prediction is that for most games in the next two years, you'll be better off with a dual-core machine where each individual core has superior single-threaded performance than with a quad-core machine where the single-threaded performance is lacking. I'll even go ahead and predict that a production dual-core Conroe system will still beat a production quad-core AMD system when the two are benchmarked against each other on popular games.

The benchmarks show that a dual-core Intel system is indeed superior to a QuadFX system for every game out there at the moment, due to Conroe's superior single-threaded performance. You're also better off with Conroe if you're just running normal office and productivity applications, with low levels of multithreading.

3D content creation and video editing

For highly multithreaded, bandwidth-intensive applications like 3D rendering and video editing—the areas where I thought that 4x4 might possibly offer a better price/performance option than a quad-core Intel system—my prediction for 4x4's prospects turned out to be a bit less accurate. It turns out that a $1,000 QX6700 beats a $1,000 pair of Athlon FX-74's hands-down in these bandwidth-intensive benchmarks, and the Intel-based motherboards are cheaper to boot.

Note that the QuadFX systems did manage to come in right behind the Intel quad-core systems in most of these highly multithreaded, bandwidth-intensive benchmarks, so they do indeed perform better on those types of applications than on any other application type. However, they still don't do well enough vs. Intel to justify their price, power consumption, and noise levels.

So what happened?

There are a few factors that probably combined to have a significant negative impact on QuadFX's debut benchmark numbers. These factors neutralized any bandwidth-related advantages that QuadFX might've had over Kentsfield.

First, it appears that content creation apps are currently CPU-bound, and not bandwidth-bound. So Kentsfield is balanced enough that its superior per-core performance gives it the edge over QuadFX even in bandwidth-intensive applications, in spite of the latter's extra system bandwidth. This situation may change, however, by the time AMD moves to four cores per socket with K8L.

Second, all of the reviews were run using Windows XP. XP's support for the type of non-uniform memory architecture (NUMA) that QuadFX uses is pretty poor, and this certainly had a non-trivial impact on QuadFX's showing. Windows Vista has a much-improved, NUMA-aware scheduler, and there's already evidence that this will have an impact on QuadFX. An Italian site actually benchmarked QuadFX under Windows Vista RC2, and the system saw a real boost on high-bandwidth/highly-threaded benchmarks versus XP-based runs of those same benches. The QX6700 still wins, but the results are closer.

NUMA-related issues are surely why dual-core, single-socket Athlon systems beat the quad-core, dual-socket QuadFX systems on some benchmarks. The single-socket systems had better average memory latencies because there was only one pool of DDR2.

Finally, it should be noted that there's only one motherboard option for QuadFX, so there's no way to control for the possible effects of the board implementation in the results. You haven't read enough motherboard reviews if you don't think that two different motherboards from two different vendors based on the same chipset and hardware can perform differently. Note that I'm not blaming QuadFX's poor showing on Asus—not at all. But I am pointing out the possibility that this could've been one small negative factor in the overall picture.